Low solar transmittance coatings are well known in the art. Typically, they include one or two layers of infrared-reflective film and two or more layers of transparent dielectric film. The infrared-reflective film, which will commonly be a conductive metal like silver, gold, or copper, reduces the transmission of heat and light through the coating. The dielectric film is used to antireflect the infrared-reflective film for part of the visible light, and to control other properties and characteristics of the coating, such as color and durability. Commonly used dielectric materials include oxides of zinc, tin, indium, bismuth, and titanium, among others.
The production of such layer stacks involves thin films of precisely uniform optical properties. Most commercially available coatings for management of visible solar light and flow of heat in and out of windows have one or two silver layers each sandwiched between two coats of transparent dielectric film. Increasing the number of silver films in a coating can be used to increase its selectivity to transmit and reflect spectral parts of the total solar radiation and increase reflectivity for other far infrared radiation. However, this can also reduce the visible light transmission of the coating, and/or negatively impact the color of the coating, and/or decrease the durability of the coating. Perhaps for these reasons and the requirements for high precision of the coating process, low solar energy transmittance coatings with three silver layers did not find much place in the market historically.
Some triple-silver low solar transmittance coatings are now available commercially, and others are known from the patent literature. While some of these coatings have been quite advantageous, there is room for continued development. For example, it would be advantageous to provide new triple-IR-layer film stacks that can provide particularly low solar energy transmittance resulting in a low solar heat gain coefficient, while at the same time achieving good visible transmittance. Further, it would be desirable to provide a triple-IR-layer coating that is optimized for providing particularly low solar energy transmittance in combination with high visible transmittance and other desired properties (e.g., desired color properties) when laminated. For example, it would be desirable to provide such a triple-IR-layer coating that can provide controlled property changes (e.g., small or otherwise controlled optical property changes) upon being laminated. In some cases, it would be desirable to provide a triple-IR-layer coating that is durable to heat-bending and also exhibits the foregoing properties and characteristics. In some embodiments, it would be desirable to provide a triple-IR-layer coating that is optimized for use in glazing units equipped with additional coatings on the surfaces exposed to an outdoor environment, an indoor environment, or both, while at the same time exhibiting some or all of the foregoing properties and characteristics.